The present invention relates to a continuous process for the production of gel free polymers, to the polymeric products produced by the process, to powder and liquid coating applications containing the polymeric products made by the process, and to powder and liquid coatings containing such polymers.
Continuous processes for the production of polymers are well known in the art. However, many of the processes used to date to produce polymers for industrial use suffer from significant limitations including high cost, significant gelation problems when utilizing epoxy-containing monomers or high levels of acrylic monomers, poor incorporation levels of particular monomers, and an inability to produce polymers that can be utilized in weatherable and non-yellow coating applications.
U.S. Pat. No. 4,414,370, issued to Hamielec et al., discloses a continuous bulk polymerization process for polymerizing vinylic monomers to prepare low molecular weight polymers employing thermal initiation at reaction temperatures from 235xc2x0 C. to 310xc2x0 C. and residence times of at least 2 minutes in a continuous stirred reactor zone.
U.S. Pat. No. 4,529,787, issued to Schmidt et al., discloses a continuous bulk polymerization process including an initiator for preparing low molecular weight, uniform polymers from vinylic monomers at short residence times and moderate reaction temperatures to provide high yields of a product suitable for high solids applications.
U.S. Pat. No. 4,546,160, issued to Brand et al., discloses a continuous bulk polymerization process for polymerizing acrylic monomers to prepare low molecular weight, uniform, polymers for use in high solids applications which uses a minor amount of initiator at short residence times and moderate temperatures.
None of the prior art teaches how to overcome the problems related to producing gel free polymers at high temperatures using continuous processes. Typically, significant gel particle formation occurs when continuous, high temperature polymerization reactions are conducted to produce polymers, particularly addition polymers such as epoxylated addition polymers. The gel formation is known to be more severe if both epoxy moieties and other functional moieties, such as hydroxyl groups, are simultaneously present in the reactor.
Moreover, epoxylated addition polymers are generally formed by the polymerization of epoxy-functional monomers together with methacrylate monomers and other selected monomers. Often the epoxy-functional monomers are themselves methacrylate monomers. Conventional high temperature polymerization methodologies have not been able to adequately solve problems encountered when producing such polymers which include low levels of incorporation of the methacrylate monomers into the final polymeric product. There remains a need for continuous high temperature polymerization processes to produce epoxylated addition polymers which overcome these shortcomings of such processes known in the art.
U.S. Pat. No. 5,256,452, issued to McMonigal et al., teaches the production of clear coatings using epoxylated polymers produced via a semi-batch process. These coatings, typically used for automobile finishes, can give a yellowish cast to the colored base coat which they cover. This is particularly a problem when the colored base coat is white. Unfortunately, clear coatings containing these epoxylated polymers produced according to U.S. Pat. No. 5,256,452 demonstrated excess yellowness when applied as either liquid or powder clear coatings over base coatings.
Finally, clear coatings containing the epoxylated polymers produced according to conventional processes have significant problems in addition to the yellowing problem described above. For example, clear coatings containing conventional epoxylated polymers also lack weatherability. When these conventional clear coatings are used in applications which expose them to extreme conditions, such as automobile coatings, they sometimes fail to provide the durability required. A need exists to produce epoxylated polymers for use in clear coatings that overcome the problems associated with conventional epoxylated polymers.
The present invention relates to a continuous, high temperature polymerization process for preparing a polymeric product, wherein the polymeric product is formed substantially free of gel particles. This is accomplished by utilizing a reactor that is filled to 100% of its usable volume. In one embodiment, the reactor is continuously charged with at least one epoxy-functional acrylic monomer, and optionally at least one non-functional free radical polymerizable monomer(s), such monomers including, but not limited to, non-functional acrylate monomers, non-functional methacrylate monomers, non-functional styrenic monomers and combinations thereof. In another embodiment, the reactor is charged with monomers which comprise at least one epoxy-functional acrylic monomer and at least one hydroxy-functional acrylic monomer, and at least one non-functional free radical polymerizable monomer(s), such monomers including, but not limited to, non-functional acrylate monomers, non-functional methacrylate monomers, non-functional styrenic monomers and combinations thereof. In still another embodiment, the reactor is charged with monomers which comprise at least one carboxylic-acid functional acrylic monomer and optionally non-functional free radical polymerizable monomer(s), such monomers including, but not limited to, non-functional acrylate monomers, non-functional methacrylate monomers, non-functional styrenic monomers and combinations thereof. The reactor in each embodiment is maintained at an effective temperature for an effective period of time to cause polymerization of the monomers to produce a polymeric product from the monomers formed substantially free of gel particles within the reactor. In each embodiment, the reactor may also optionally be charged with at least one free radical polymerization initiator and/or one or more solvents.
The present invention also relates to maximizing the conversion of all monomers in the reactor feed into the polymeric product of the present invention.
The present invention is also drawn to liquid and powder clear and pigmented coatings incorporating polymeric products of the present invention.
These and other aspects of the invention will be apparent from the specification that follows together with the appended claims.